First mower and replacement both doing the same thing first start great 2nd little hesitation 3rd time if your lucky it will turn over but starter strains heavily next try starter can not turn motor over then starter smokes

In shop they replace battery, next trip they replace starter
And I give up if someone can tell me what's wrong I will fix it

Hi,
You do not state any model or engine brand, but my guess is that you have a Briggs in need of a valve adjustment. There are YouTube videos on those. Another possibility that could be a slim one is that you have a poor engine to frame ground.
Peace,
Clarke